A radar detector is equipment that detects a laser or a microwave emitted from a speed gun used for measuring a speed of a vehicle and the like, a safety alarm device informing road information, or the like, and a use of the radar detector is legally recognized in some countries.
In the United States, the speed gun is defined to use a frequency range of an X band of 8 GHz to 12 GHz, a Ku band of 10.95 GHz to 14.5 GHz, a K band of 18 GHz to 27 GHz, a Ka band of 26.5 GHz to 40 GHz.
The speed gun uses various types using various frequencies, but since an antenna used in the radar detector is designed to respond to a specific frequency band, the antenna does not correspond to a speed gun using a frequency band other than the corresponding frequency band.
In order to detect various frequencies, when a plurality of antennas responding to different frequency bands is embedded, the size of the radar detector is increased, and the number of power supply units required for each antenna is increased, and thus the entire circuit is complicated.
Further, in the case of a radar detector used in a high frequency, since a high gain and a large bandwidth are required, a horn antenna has been used. However, the horn antenna has a limit to minimizing the radar detector due to a structural limitation.
In order to reduce in size and thickness of the radar detector, a microstrip patch antenna may be used, but the microstrip patch antenna has advantages of being manufactured in a small size and a small thickness, but disadvantages of a low gain and a small bandwidth.